President Reagan certainly understood the nature of markets.
That is they do whatever they are going to do, sometimes without a fundamental rhyme or reason. Very different from the current occupant of the White House who seems to think every uptick in the S&P is all about him, and he is not afraid to take credit for the upside and tweet about it.
https://macromon.wordpress.com/2018/04/21/president-reagan-on-the-87-stock-market-crash/